My red Scrambler currently has a JDM AX15 with 4:1 first gear, and 4:1 gears in the Dana 300.
My JDM AX15 ratios pretty much match up with the original Jeep T5 ratios.
The 4:1 Dana 300 is nice when needed, but it does limit you in some instances (i.e. need wheel speed to climb a muddy hill). Even 2nd and 3rd gears with 4:1 in the transfer case are too low sometimes. With the transmission in 4th gear, Dana 300 in low range, I am at the same ratio as 1st gear high range.
I like the 4:1 low range 90% of the time, so I am happy with it. The low speed control is great. With an automatic transmission, the 4:1 low range is not needed 90% of the time. The "lack of direct connection" in 1st gear with an automatic transmission gives you low speed control.
The tan Scrambler that I sold had a 700R4 and stock Dana 300. Most of the time, I never felt the need to add 4:1 to the transfer case. With how I use(d) both Scramblers, and how they were both set up (33" tires, 4.10 diff gears).
Depending on tire size/axle ratio's, overdrive might not even be needed. I daily drove my 1978 CJ-7 for over 10 years (304 V8, T18, stock Dana 20, 3.54 axle gears, 33" tires). Never felt it needed overdrive. The T18 was not bad behind the 304 (more power then the 258), but it would probably suck behind a 258 for street driving (2nd gear is deep, the jump in ratio from 2 to 3 is pretty large, so the lack of power would be more evident, and you are basically driving a 3 speed). Not terrible, but probably would not be "fun".
IMO, the T-18/stock Dana 20 low range was more capable then my current JDM AX15/4:1 Dana 300. I had a super deep granny gear, but could easily shift to 2nd/3rd gear and have all the wheel speed/vehicle speed I needed. Just depends on terrain.
The AX15 is nicer to drive on the street compared to the T18. With the AX15, you have 5 gears to keep the 258 in its powerband. With a T18, only 3 widely spaced gears. The T18 has long throws, true, but a stock AX15 isn't exactly a "short throw" transmission. An upgraded shift tower can make the AX15 feel like a sports car, if desired.
Depending on the model NV4500, not all are terrible. We have an older 1996 Chevy 1-ton flat bed at work. It has the 6.5 turbo diesel and an NV4500, with granny gear. I spent all day Sunday driving this truck (hauling 3-4 yards of dirt at a time), and it shifts fine, much better then any of the older "granny gear" 4 speeds. I am not an "expert" on NV4500's, but the one in this truck has short tight shifts, and 1st gear is synchronized (no need to double clutch to get it into 1st, or reverse for that matter).
Just depends on what you are used to driving.
I almost wonder if I would be happier with an NV4500 and stock low range? I could upgrade my red Scrambler and keep the AX15 for my green Scrambler (if ever needed)